The present invention relates to a suction unit provided to a delivery unit in a sheet-fed rotary printing press, which draws a printing product being conveyed in a slidable contact state by suction, and decelerates it.
In a sheet-fed rotary printing press, a printing product (to be referred to as a sheet hereinafter) printed by a printing unit is transferred from the grippers of an impression cylinder to the grippers of delivery chains, conveyed, released from the grippers at a convey terminal end, and dropped onto a pile board and stacked there. In this delivery unit, as the sheet to be conveyed is merely gripped at its leading end by the grippers, the trailing end of the sheet may flap. When the gripped sheets are released and dropped, the ends of the stacked sheets may not be aligned since traveling inertia remains in the sheets.
In order to prevent this, a countermeasure is proposed as shown in Japanese Utility Model Publication No. 7-26288. According to this reference, a plurality of suction wheels each having suction surfaces are aligned near the convey terminal end in the widthwise direction of the sheet (a direction perpendicular to the convey direction). A sheet released from grippers is attached to the surfaces of the suction wheels so that the sheet convey speed is decreased. In this suction unit, the suction wheels that rotate at a peripheral velocity lower than the printed sheet convey speed are formed upstream of the delivery unit in the delivery direction. The suction surfaces connected to a suction air source are formed in the circumferential surfaces of the suction wheels to draw a sheet by suction while coming into slidable contact with the sheet.
When the suction unit having the above arrangement is used in a perfector, if the suction wheels are arranged at positions corresponding to an image printed on the lower surface of the sheet, the suction surfaces of the suction wheels damage the image printed on the sheet to degrade the printing quality. For this reason, the suction wheels must be arranged to correspond to non-image areas where an ink is not attached to the sheet. In the non-image areas, the number of images changes depending on plate making for the image (image assignment in the widthwise direction of the sheet). Accordingly, the number of suction wheels must also be changed in accordance with the number of images.
In the conventional suction unit of the sheet-fed rotary printing press, since a drive shaft extends through the suction wheels, the suction wheels cannot be removed from the drive shaft. If some wheels may not be used as the result of a change in image plate making, unnecessary suction wheels must be moved to the outer side of the sheet width, which is cumbersome.
In a printing press serving as both a perfecter and a single-sided printing press, when double-sided printing is to be performed, suction wheels each having a width smaller than the width of a non-image area are required. In single-sided printing, when high-speed printing is to be performed on a thick sheet, wide suction wheels having a large suction force are required. When these suction wheels are required, the entire assembly of the suction wheel is exchanged. Alternatively, both suction wheels required for double-sided printing and single-sided printing are mounted in the suction wheel assembly, and an unnecessary suction wheel is moved outside the sheet in the sheet widthwise direction, as described above.